We would probably need to see your image (along with the embedded EXIF data so we can see the camera settings that were used for it.)
But I'll offer a few general tips...
The default shooting mode of most bodies is to use "One Shot" mode. Canon bodies have a "One shot" mode, an "AI Servo" mode, and then a special mode called "AI Focus" which really just means the camera evalutes whether it should use One Shot vs. AI Servo mode on the fly.
In "One Shot" mode, the camera uses "Focus Priority" and does NOT focus continuously for moving subjects. Once it locks focus on something it's ready to shoot but it will not adjust the focus for a moving object. This means that at some point your subject was in focus... but has since moved from that position. You can fix this by switching to AI Servo mode.
In "AI Servo" mode, the camera WILL focus continuously... as your subject moves, the camera will continue to adjust focus... but the camera also uses "release priority" when in AI Servo mode. So whereas in One Shot mode (which uses "focus priority"), if you press the button all the way, the camera will not actually take the shot until it can lock focus first (which is why some people think their camera is malfunctioning when it wont take a photo in a very dark room -- because it can't lock focus) -- in "AI Servo" mode (which uses "release priority") the camera WILL take the shot when you fully press the button and it will do this whether it has had time to focus or not (so that's an important detail to remember). Half press to get the camera to lock focus and keep tracking your subject with your focus point (and it will continuously focus)... then fully press the button to take the shot .
The EF-S 55-250mm lens does not have particularly fast focusing motors... the STM lenses are faster and the USM lenses are the fastest. Action photographers will specifically seek lenses with fast focusing motors... without a fast motor, sometimes it may not be possible for a lens to track focus adequately -- however Canon does use "predictive" focus when tracking an object whose distance to your camera is changing at a uniform rate.
Also... you'll want to give yourself a nice broad depth of field so that a small amount of focus error wont really impact the final outcome. It will be easier to keep things in acceptable focus at f/11 (or even f/16) than it is when you're using a lower f-stop such as f/4 or f/5.6.
BTW, Canon does not recommend just leaving the camera in AI Servo mode. It turns out there are some nuances of the way this works which can trick the camera into thinking there was movement and altering focus when taking a non-action shot... resulting in missed focus. Use "One Shot" when shooting non-action. Use "AI Servo" when shooting action. I don't actually recommend "AI Focus" (that's the mode that auto-decides if it's an action shot or not) BECAUES there's a slight delay while the camera evaluates which mode to use and that can cause you to miss the "decisive moment" to grab the shot.
Hope this helps... I'll try to find the YouTube videos that Canon has which explain how your auto-focus system works. It is quite informative and tells you more about how your camera "thinks" when it comes to focus.
Tim Campbell
5D III, 5D IV, 60Da